Heat is often created as a byproduct of industrial processes and is discharged when liquids, solids, and/or gasses that contain such heat are exhausted into the environment or otherwise removed from the process. This heat removal may be necessary to avoid exceeding safe and efficient operating temperatures in the industrial process equipment or may be inherent as exhaust in open cycles. Useful thermal energy is generally lost when this heat is not recovered or recycled during such processes. Accordingly, industrial processes often use heat exchanging devices to recover the heat and recycle much of the thermal energy back into the process or provide combined cycles, utilizing this thermal energy to power secondary heat engine cycles.
Waste heat recovery can be significantly limited by a variety of factors. For example, the exhaust stream may be reduced to low-grade (e.g., low temperature) heat, from which economical energy extraction is difficult, or the heat may otherwise be difficult to recover. Accordingly, the unrecovered heat is discharged as “waste heat,” typically via a stack or through exchange with water or another cooling medium. Moreover, in other settings, heat is available from renewable sources of thermal energy, such as heat from the sun or geothermal sources, which may be concentrated or otherwise manipulated.
In multiple-cycle systems, waste heat is converted to useful energy via two or more components coupled to the waste heat source in multiple locations. While multiple-cycle systems are successfully employed in some operating environments, generally, multiple-cycle systems have limited efficiencies in most operating environments. In some applications, the waste heat conditions (e.g., temperature) can fluctuate, such that the waste heat conditions are temporarily outside the optimal operating range of the multiple-cycle systems. Coupling multiple, discrete cycle systems is one solution. However, multiple independent cycle systems introduce greater system complexity due to the increased number of system components, especially when the system includes additional turbo- or turbine components. Such multiple independent cycle systems are complex and have increased control and maintenance requirements, as well as additional expenses and footprint demands.
Therefore, there is a need for a heat engine system and a method for recovering energy, such that the system and method have an optimized operating range for a heat recovery power cycle, minimized complexity, and maximized efficiency for recovering thermal energy and producing mechanical energy and/or electrical energy.